202 SUPPLEMENT TO THE 



Rhynchonella decemplicata, Sow. Dav., Sil. Mon., PI. XXIII, figs. 20 — 24 ; Sil. 



Sup., PI. XI, fig. 27. 



This species is fully described at p. 177 of my ' Silurian Monograph,' and I refer to 

 it again merely to say that Mrs. R. Gray has found the species in the Lower Llandovery 

 or Mullock beds, at the head of Thraive Glen, in Ayrshire. 



TRETENTERATA. 



Genus — Lingula, Bruguiere, 1789. 

 131. Lingula Canadensis, Billinfjs ?. Dav., Sil. Sup., PI. XVII, fig. 1. 



Lingula canadensis, Billings. Geol. Survey of Canada, Fossils, vol. i, p. 114, fig. 95, 

 June, 1862. 

 — — ? Bav. Geol. Mag., new series, vol. iv, p. 16, pi. ii, figs. 4, 



4 a,b,c, 1877. 



Of this large and beautifully sculptured Lingula, Mrs. R, Gray has obtained one 

 incomplete example. It was from the Breccia-conglomerate of Balcletchie, near Girvan, 

 in Ayrshire. The conglomerate rests upon the compact dark-grey rock at Balcletchie, 

 and both are considered by Prof. Lapworth to be of Llandeiio age. 



It is not possible to describe this fine fossil in a complete manner, because the two 

 anterior thirds of the valves are alone preserved. It, however, so nearly agrees in shape 

 and sculpture with the fossil described and figured by Billings under the name of L. 

 Canadensis from the Hudson-River group of Anticosti, that I have thought it preferable 

 to leave it provisionally under that designation.-^ 



Lingula Canadensis is of a quadrate or sub-parallel elongated shape, posteriorly 

 acuminated, broadest anteriorly, sides almost straight, front slightly curved, with broadly 

 rounded angles ; the smallest valve is much flattened anteriorly, and but slightly 

 convex posteriorly or towards the beak ; the larger valve is very much deeper and more 



^ I regret not to have been able to make a direct comparison of our Scottish shell with the Canadian 

 type. No specimen of the Canadian species could be found in the Museum of the Geological Survey of 

 Canada at Ottawa. Mr. Whiteaves kindly made every search but in vain, to discover the type. 



